We did the same thing. It took me a few iterations to get the library right, but overall I used approx 10 billion tokens here across a codex and Claude max plan

The first iteration was a rewrite using codex /goal but it ended up producing junk

The second iteration was fable controlling gpt-5.5 agents to write the code with really strong acceptance tests. This pushed the library in the right direction and is basically what you see here today